In its natural environment, marijuana is an annual, meaning that it evolves from seed to seed-producer in one season, before dying off. And given that marijuana grows from a few centimetres to 2 or even 3 metres during this 6 month period, you can see how vital and energetic its vegetative growth can be.
Of course as marijuana cultivators, we value quantity and quality of bud above height of plant. To get the best bud, we need to get the vegetative growth stage of our marijuana as healthy and vigorous as possible.
In outdoor grows the vegetative growth stage lasts between 4 and 6 months; in a grow room, in soil, from 1-2 months. Hydroponically, a well rooted cutting can be grown for one week before putting into flower – this works well with a planting distance of 6 plants per metre. Obviously the period of growth all depends on your style of marijuana grow. The superfast autoflowers almost omit vegetative growth stage entirely.
How to make sure your marijuana plant grows well
Here are the basic facts that you need to know for successful marijuana cultivation:
Apart from autoflowers, marijuana is a photoperiod plant i.e. it is triggered into flower by the shortening of daylight as summer moves to winter. As long as there are less than 12 hours of darkness, the marijuana grower convinces the plant to remain in vegetative growth. Conversely, by increasing the hours of darkness to 12 hours or more, the plant can be forced into flowering whilst still little more than a well rooted seedling.
For the best vegetative growth, give plants 6 hours of darkness per “day”: they can cope with 24 hours of light, but many cannabis growers believe marijuana benefits from a rest period from both light and heat.
For indoor marijuana grows, this fact can be manipulated to varying effects e.g.
- mothers can be kept in vegetative stage beyond the annual life cycle of a natural plant
- well rooted cuttings can be put into flower very quickly for a sea of green (SEO) style grow.
- Even an outdoor grower can force a plant into flower by artificially creating a 12 hour day using black bin bags. I have to say this is probably too high maintenance for most growers.
You’ll need to use a timer like this one to make sure you provide the right hours of darkness to your plants. It will come in particularly handy when you flip your indoor grow room into flower as then you NEED to make sure you give your cannabis plants 12 hours of darkness at regular periods of time. Thinking you will remember to turn your lights off is a no-brainer. Trust me it won’t happen and your plants will suffer stress from irregular light patterns. That means lower end yield. FACT.
Marijuana plants are photophilous: they love and need high density light to thrive. Plant growth occurs due to the process of photosynthesis, whereby the plant converts carbon dioxide into organic material using energy derived from light. Therefore the quality and quantity of light available to the plant directly effects the amount of growth. Outside growers are both blessed and cursed by the best light source
sunlight – whilst marijuana grow rooms replicate natural light intensity through artificial means: HID, T5, CFL and LED lights. Strong light is not enough however as different light wavelengths effect growth and flower: the indoor grow room needs to replicate the light spectra necessary for growth – and then again, for flower.
Humidity and Temperature
Despite being sun lovers, not many marijuana strains enjoy high temperatures and in the outdoors, vegetative growth will stall at anything above 38ºC as the plants struggle to cope with transpiration rates and recovery rather than put energy into growth. At 34ºC they will be putting on maximum vegetation.
For the indoor grow room, particularly one using HID lights, its essential to use humidity and temperature gauges, combined with fans and extractors to maintain a healthy growing temperature range of between 21-29ºC. Humidity should be relatively dry (60-70%) as this encourages the plant to produce a protective layer of resin over the leaves (its own sunscreen). If the grow room is too wet, the leaves become wider and less resiny. Too dry however and you stress your marijuana plants.
Night temperatures should be between 16-20ºC.
Extraction & Ventilation
In its natural state, the marijuana plant enjoys fresh air, plenty of carbon dioxide and breezes which stimulate strong stem growth. Inside, you need to replicate this environment by use of fans, extractor systems and even C02 machines for the best vegetative growth. Read our article on ventilation for more details.
PH and watering
Marijuana plants need water with a pH of 5.8 – 6.3 if grown hydroponically, or 6.2-6.8 if grown in soil. PH is important as different levels of pH affect the amount of specific nutrients that can be absorbed by the plant. Using water outside this range will result in nutrient block outs and a range of problems as the plants become unable to absorb essential nutrients. (see nutrient problems).
A pH can be one of the most important tools for both the indoor grow room and an outdoor cannabis grow. Unless you’re really strapped for cash, don’t bother with a really cheap pH pen (under $15.00) they won’t hold their ability to read pH at all. A good pH pen on the other hand will keep going, grow after grow. Read this article here on why we think pH is so important when growing cannabis
As to how much water to give your marijuana plants? Growers have differing opinions: some like to let the soil or medium almost dry out and water just before the leaves begin to droop, others prefer regular amounts daily. We say its important to understand the wet/dry cycle when growing cannabis!! Frequency of watering will depend on the growing medium that you use. Virtually soil-less mixes with a high percentage of perlite and clay pebbles will demand more frequent watering than a well retentive soil. Watch your plants: they will tell you if they need more water than you are giving them. And the rules are obviously completely different if you are considering growing hydroponically. Probably the biggest danger however is over-watering: it will lead to root rot and eventual death.
Marijuana is a hungry plant. If you are growing in specialist cannabis compost you will find that this contains some added nutrients, but whatever your medium you will need to give your cannabis some nutrient feed, and it is important to get the ratio of nitrogen-potassium-phosphorous correct for vegetative growth. Always spend the extra money on a specialist marijuana grow food, and one refined for your growing medium. N:P:K for vegetative growth should be 2:1:1 as the plants use double the amount of nitrogen during this stage.